15.7.3. XML Schema Definition Language

The W3C XML Schema Definition Language is a way of describing
and constraining the content of XML documents.

The XML Schema specification consists of three parts. One part
defines a set of simple datatypes, which can be associated with XML
element types and attributes; this allows XML software to do a
better job of managing dates, numbers, and other special forms of
information. The second part of the specification proposes methods
for describing the structure and constraining the contents of XML
documents, and defines the rules governing schema validation of
documents. The third part is a primer that explains what schemas
are, how they differ from DTDs, and how one builds a schema.

XML Schema introduces new levels of flexibility that may
accelerate the adoption of XML for significant industrial use. For
example, a schema author can build a schema that borrows from a
previous schema, but overrides it where new unique features are
needed. XML Schema allows the author to determine which parts of a
document may be validated, or identify parts of a document where a
schema may apply. XML Schema also provides a way for users of
e-commerce systems to choose which XML Schema they use to validate
elements in a given namespace, thus providing better assurance in
e-commerce transactions and greater security against unauthorized
changes to validation rules. Further, as XML Schema are XML
documents themselves, they may be managed by XML authoring tools,
or through XSLT. The implementation of XML Schema in Virtuoso is
based on the W3C XML Schema Specification .